Radio receiving apparatus



June 10, 1930. N U 7 1,762,186

RADIO RECEIVING APPARATUS Filed April 20 1925 "2 Sheets-Sheet 1 rm Q June 10, 1930' I 1 B. B. MINNIUM ,186

. RADIORECEIVING APPARATUS Filed April 20, 1925 2 Sheets-Sheet .2

Patented June It), 1930 UMTEJB smres ar-Eur creme BYRON B. MINNIUM, OF=CHICAGO, amnnors, Lassie-Non, BY nsnn ASSIGNMENTS, To 1 STORY & TGLARKIRADIO oon1=.,=er CHICAGO, rumors, =A CRP'0BA TI0N or DELA- WARE Ap ilieat ionffiied'Apri1'20, 1925. Serial No. 24,399.

This invention relatesto radio receiving apparatus, and more particularly 'to apparatus of'this kind'in which means are provided for tuning the receiving set and 'in which amplifying meansare provided, and in which there is some tendency'tow'ardthe local setting up of sustained oscillation, which, of course, may interferewith the proper operation of the "apparatus, inas- 0 much as suchtac'tion has atendency to interfere with the incoming signal, "or even to entirely blanket the incoming signal, so to speak, and thereby prevent the proper operation of the, apparatus. Y

Generally stated, therefore, the object of the invention is'to provide a novel and im proved circuit arrangement and tuning means which can be adjusted in a 'mann'er to more or less change the capacity employed to prevent-the said undesirable selfoscillation of the receiving set, thereby to obtain certain beneficial results, as will hereinafter more fully appear.

It is also an object to provide ccrtaindetails and'features of construction, and'co'mbinations tending to increase the general efiiciency and the desirability of a radiofrequen'cy amplifying arrangement of this particular character;

To the foregoing and other useful ends,

theinvention consistsin the matters hereinafter set forth and claimed,- and shown in the accompanying drawings, in which,-'.

Fig. 1 is a diagram of aradio-receiving apparatus embodying the principles olf 'the invention.

Fig. .Zis a simplified diagram,-using the ordinary I showing the theory and the mode of operation of the invention. 1

Fig. 3 :is a 'botom View of two'of the adjustable condensers shown at the left in Fig. 1. e o t Fig. 4 is an axial section on line 44 in Fig. 3. V r

Fig. 5 is a transverse section on line 5--'5 in Fig. 3.

As thus illustrated, the hook-up or cir- Y 'cuit arrangement shown in Fig. 1 is in a general way an ordinary one, involving a three-stage vacuum tube amplifier. 'aer'ial 1 may be of any suitable. "character Wheatstone bridge arrangement,

' ean-1o neon-WING APPARATUS The and is grounded through the primary '2 of the transformer or repeating coil,"as shown. The secondary e011 3 has'one terminal connected to the grid 4 of the first vacu'u'm' tube, and has the other "terminal connected to the stopping condenser 5 of any suitable character. The other terminal of'the condenser 5 is connectedto the plate 6 of the vacuum tube, and the filament 7 of the tube ordinary manner. The second stage of amplification is of similar'character, it will be seen, and a description of the circuit ar rangement of one lamp or vac'uumtiibe will be sufficient.

Fontuning purposes, two adjustable condensers 8 and 9 are "connected in series be- I tween the terminals of the secondary *coil ment'? and carrie'dover to the middle point T 11 0f the capacity shunt thus formedin parallel with the "secondary coil 3 of the has its terminal connected to the batteries shown at the right of the diagram, in the transformer 01-" repeating c'oil. The pri- 'mary coil 12 of the next transformer or repeating coil, of the second stage of ampli- 1 fication, is connected in'circuit as showrns'o that the c0il'3 is inthe input-circuit ofth'e lamp or vacuumitu'be', 'while the coil 12 is in-the output-circuit of said lampor tube.

' *VViththis arrangement there'is a tendency toward oscillation, as previously stated, owing to a'sort of feedback from the plate 6 to the grid t,during the reception of the radiosfrequency signal, but with the arrang'emen't shown, involving the use of capacities 5 and 8 and 9, and'the ca pacity H between the grid and the plate 6, the harmful and undesirable oscillation is prevented.

As shown by :the 'W-heatsto'ne bridge arrangement in Fig; 2 there is capacity in each arm ofthe bridge,sothat all fourfa'rms of the bridge contain capacity in the proper ratio to P e t the said 'feed bak'of ener y from the plate to the grid of the "lamp O1- vac'uurn tube. With such arrangement, it

= shown and described.

'densers are adjustable.

is found that an electrical disturbance or voltage across the points 13 and 1 1 will have no effect upon the points 15 and 16 or input terminals. In other words, the Wheatstone bridge arrangement is balanced, so to speak, and the points 15 and 16 remain at the same potential, so far as any electrical disturbance across 18 and 14 is concerned. In this W'heatstone bridge arrangement, as shown, there is employed as one capacity for one arm or side of the bridge the grid-t0- plate capacity 4 and 6, and the other three arms'of the VVheatstone bridge have the condensers 5, 8 and 9 located therein, as The capacity 8 and 9 is employed for tuning the input circuit of the lamp or vacuum tube, as these con- The condensers 8 and 9 can be separately adjustable, or they can be mounted on the same shaft, or geared together, whereby the motion of one is governed by that of the other, so that the two condensers may be varied together by a single'control, but preferably in such a way as to at least approximately'maintain a constant capacity ratio.

One advantage of the invention, therefore, is that its operation is independent of the voltage distribution along the coil 3,that is to say, since the filament of the amplifier tube is connected to the physical center of the input capacity, as shown, it is therefore connected to the electrical center of the input circuit, and hence with this arrangement there is no. danger that the variation in voltage distribution along the coil may upset the balance of the VVheatstone bridge arrangement thus involved in the hook-up or circuit arrangement shown and described, which is illustrative of one form of the invention.

As a further advantage, it has been found that when two capacities are connected in series, the resultant capacity variation is so greatly increased over that usually obtainable that the size of the inductance .3 may be greatly increased, and the size of 8 and 9 correspondingly reduced, and still cover the wave length range over which the circuit is ordinarily tunable. One advantage of this is that the voltage applied to the grid of the vacuum tube amplifier is much greater than is obtained by the ordinary arrangement, thus lnsuring greatly lncreased amplification for each stage.

It Wlll be understood, of course, that in practice the different repeating coils or transformers will be so arranged, relatively to each other, that they will not affect each other, inductively, thereby to insure against interference between them. Furthermore, it will also be observed that with the circuit arrangement shown and described the grid of each lamp or vacuum tube has no physical connection to the filament of the lamp or tube, and hence has no physical connection to any source of direct current, and hence there is no possibility of any such source impressing its voltage on the grid. .Vith this circuit arrangement it is found that the tone quality is also improved, over that obtained with the ordinary circuit arrangement, as the tone appears to be clearer and better, which means better and more accurate reproduction.

Now, with a circuit arrangement of the character shown and described, involving the use of transformers between the first 'and second tubes, and between the second and third tubes, as shown, there is some difference, of course, in the action of the transformers, when high frequencies or short wave lengths are used, from what happens when low frequencies or long wave lengths are employed. In other words, the repeating coils or transformers between the tubes work better with the high frequencies than they do with the low frequencies, and the amplification is better with the high frequencies than with the low frequencies,

as is well known. Therefore, in order to compensate for the decreased efficiency of the repeating coils or transformers, when low frequencies or long wave lengths are used, the invention contemplates the use of adjustable capacity, in the bridge containing the condensers 8 and 9, for the different adjustments necessary for relatively long wave lengths, thereby to cause a slight feed back in the circuits, to the grids of the tubes, thus causing the amplifying circuits to work better than would be the case if the capacity in said bridge were exactly the same for long wave lengths, as well as for short wvave lengths. The longer the wave length,

therefore, the greater will be the unbalancing effect as between the condensers 8 and 9,'that is to say, for the short wave lengths these two condensers will have an adjustment which results in a certain condition of the capacity in this bridge, but for longer wave lengths the two condensers will be somewhat unbalanced, and for still greater wave lengths the two condensers will be still more unbalanced, in order to bring about the desired feed back and increased action of the vacuum tubes for the longer wave lengths.

For the, unbalancing of the bridge in the ,manner explained, and suitable arrangement can be employed. As a matter of further and special improvement, however, the con denser mechanism shown in Figs. 3, 4 and 5 can be employed for this purpose. As shown, the two condensers 8 and 9 have their movable plates mounted on a single shaft 1'7, the stationary plates being suitably mounted on the frame 18 of the con-denser mechanism. With this arrangement, the two condensers are simultaneously adjustable, in the well known manner, to tune Lil the apparatus for different wave lengths. In order tounbalance the bridge, however as between the two condensers, one, movable plate 19 of thecondenser 8 is cut awayto form an edge 20, which is curved-in the manner shown, so that when the shaft 17 is rotated in the direction of the arrow shown in Fig. 5, for the shortest wave lengths,the movable plates will all be above the Stationary plates; but when the rotation is continued, in order to bring the movable plates partially between the stationary plates, the end or corner portion 21 ofi the said cut-away movable plate will" descend a distance before the curve 2@ begins to subtract from this plate, so that thesubtraction is progressive, so to speak, and: whereby the unbalanced effect as between the two condensers is also progressive and re'a'ches its maximum when the movable plates are entirely between the stationary plates; for at-such time there is subtracted f-rom oneof the movable plates the area included between the curve and the curve 22, which latter represents the curved edges of all the movable plates, as well as the curved edges'of the stationary plates. When the movable plates are all above the stationary platesfor the shortest wave lengths, if there be some difference between the capacity of the two condensers, because ofthe fact that the mutilated plate 23 having the edge 2O has its straight upper edge 24 removed for the distance between the points 25 and 26, it is compensated for by adjustment of the condenser. 5 to insure the, exactly balanced condition of the bridge desirable: for the short wave lengths or high frequencies. I j

Of course, the invention contemplates the adjustment of the capacity of the bridge containing the condensers-8 and 9-, for the of, it will'b'e understood tl'i at the difference in area between the two cond'ensers and; the difference in capacity can be a'ccoinplished' in any suitable or desired ma n'neri Thus-a differential condenser is provided, the condenser being made in two sections, so to speak, and

the differential between the two condensers being variable, andbeing greater for they longest wave lengths than for shorter wave lengths, in the manner explained; Of course, as shown and described, it is one of the movable plates of the condenser which is cut away to reduce its area, butitwill be understood that any plate'or plates of p the condenser can be reduced in; area-,to obtain.- the desired variable differenti ali between the two simultaneously adjustable condens ers, if such is necessary or desirable.

Nowit will beunderstood that the normal operation or functioning of? the Vvheatston'e bridge arrangement, as illustrated in Fig.2,

requires that this W'heatstone bridge be ball a=ncecl, which meansthat the ratlon of 8' to 9 must be the same as the ration of As, 6 to. 5, or that the ration of 8 to 45, 6 must be the same as the ratio of'9 to 5, in: order to ob tain the balanced characteristic of the Wheatstone bridge arrangements 'Ehen, as explained, in order to obtain the desired feed back, to improve.='the-receiving action sired feed back to improve the actionof the amplifying means. -Of course, any one er all of the vacuum tubes'or lamps shown and described, except the last, can be made sub ject to this feed"back, and, of course; ill 01- der to prevent any of the'feed baclrf'rom reaching the aerial, the unbalanced Wheat stone bridge effect can be confined to the second vacuum tube or stage of amplification and to any subsequent stagesof amplification, instead ofbeingappl ied to the first stage of amplificat'ion shown at the lett 'of Fig. 1 of the drawings-.- Bllii,'ll1 any event, the invention contemplates a VVheatstone bridge arrangement thenormal balance of which can be disturbed, more or less, toprcvide a feed back which will improve" the receiving action in the manner explained when the longer wave lengths are employed The VVheat stone bridgearrangement, of course, may be employed foran-y suitable self-oscillation, as explained, but it can be used for any suitable or desired purpose,'togethenwith the means for disturbing or unbalancing the Zhea'tsto'ne bi'idge. without the simple bridge containing the condensers 17 and 18', is merely a transverse bridge between the two parallel conductors 19 and or desired purpose. shown, it is em e ployed to counteract the tendency toward.

20, and between the two paralleli conductors 21 and "22, and-are different from the socalled VVheatstone bridge arrangei'n'ent; involved in the apparatus, which \Vheatstone bridge arrangement is. shown diagramma'ti cally in Fig. 2 of the drawings; Of course", so far as the p ov sion of Se1f0sci1l' on= is concerned, the condensers 8 and 9'may have the same capacity, and in such case the condenser 5 will be adjusted to equal the capacity of 4 and 6, whereby the ratio between 8 and 9 will be the same as the ratio between 4, 6 and 5 and the ratio between 8 and a, 6 will be the same as the ratio between 9 and 5, for the reasons explained. However, in order to provide a slight regenerating effect, or feedback, as explained, one of the adjustable condensers can be given a slightly different capacity, such as the condenser 8 has by reason of its abbreviated plate '23, as previously explained.

It will be seen that the unbalancing of the VVheatstone bridge arrangement, by the simultaneous adjustment of the condensers 8 and 9, is automatic, so to speak, inasmuch as this unbalancing is incidental to the tuning of the apparatus by adjustment of these condensers. The condenser 5 can beset in such fixed adjustment thereof as will serve the purpose for all adjustments of the condensers 8 and 9, so that in tuning the apparatus for different wave lengths, it is only necessary to adjust the condensers 8 and 9, as by this adjustment alone the progressive unbalancing of the Wheatstone bridge is accomplished in the manner explained. In

other words, theunbalancing of the bridge is unavoidable, and is an unavoidable incident to the tuning of the apparatus by adjustment of the condensers 8 and 9, and the unbalanoing is not accomplished by any separate and deliberate or special act on the part of the user. In this way the degree of unbalance for each wave length is predetermined, so to speak, by the fixed, relative formation of the two condensers 8 and 9, as they are on the same shaft and their structural relation to each other cannot be changed. Hence, when the apparatus is manufactured, the condenser 5 can be ad justed and set as desired, and the user will then simply simultaneously adjust the two condensers 8 and 9, and in this way the apparatus is originally assembled and made in a manner to insure the unbalancing desired, when the condensers 8 and 9 are adjusted in one direction, and the progressive return of the bridge to acondition of more balance when. these condensers are adjusted in the opposite direction.

Withoutdisclaiming anything, and without prejudice to any novelty disclosed, what I claim as my invention is:

l. A radio receiving apparatus comprising a vacuum tube or lamp having a filament and a grid and a plate and elements forming in efiect a Wheatstone bridge arrangement, with capacity in each arm of the bridge, one such capacity being formed by the grid-to-plate capacity of said lamp or tube, having a secondary of an inductive coupling from an aerial to an input circuit 1,7e2,1se

of the lamp connected between opposite points on said bridge, having an output circuit of the lamp connected between the other two opposite points on said bridge, and having tuning instrumentalities relatively formed and adapted for automatically and unavoidably causing an unbalancing of said bridge to a predetermined extent suitable for the lower frequencies or longer wave lengths, in the tuning operation, thereby to produce some feed back and a consequent better action of the vacuum tube for the longer wave lengths.

2. A radio receiving apparatus comprising a vacuum tube or lamp having a filament and a grid and a plate and elements forming in effect a Wheatstone bridge arrangement, with capacity in each arm of the bridge, one such capacity being formed by the grid-to-plate capacity of said lamp or tube, having instrumentalities for unbalancing said bridge for the lower frequencies or longer Wave lengths, thereby to produce some feed back and a consequent better action of the vacuum tube for the longer wave lengths, said instrumentalities comprising two condensers mounted on the same shaft, one condenser forming the capacity of one arm and the other condenser forming the capacity of another arm of said VVheatstone bridge arrangement, with one of the movable plates of one condenser of less area than the others and formed to progressively unbalance the two condensers as the shaft is turned in a direction to tune the apparatus for the longer wave lengths.

3. A radio receiving apparatus comprising a vacuum tube or lamp having a filament and a grid and a plate and elements forming in effect a Wheatstone bridge arrangement, with capacity in each arm of the bridge, one such capacity being formed by the grid-to-plate capacity of said lamp or tube, having instrumentalities for unbalancing said bridge for the lower frequencies or longer wave lengths, thereby to produce some feed back and a consequent better action of the vacuum tube for the longer wave lengths, said instrumentalities comprising a pair of adjustable condensers each forming the capacity of one arm of the Wheatstonc bridge arrangement and relatively formed to cause one condenser to have more capacity than the other, when both are adjusted for the longer wave lengths, but having substantially the same capacity when both are adjusted for the shortest wave lengths.

4. A radio receivingapparatus comprising a vacuum tube or lamp having a filament and a grid and a plate and elements forming in effect a Wheatstone bridge arrangement, with capacity in each arm of the bridge, one such capacity being formed by the grid-toplate capacity of said lamp or tube, having instrumentalities for unbalancing said bridge for the lower frequencies or longer Wave lengths, thereby to pr'oduce some feed back and a consequent better action of the vacuum tube for the longer wave lengths, said instrumentalities comprising two condensers 7 same circuit, having a tube connected to the densers is variable automatically by the adelectrical circuit connection between the two condensers, the condensers being connected in series, and the condensers being so relatlvely formed that the ratio between the conjust-ment thereof in unison.

6. In radio apparatus, the combination of instrumentalities forming in efiect a YVheat stone bridge arrangement having condensers in two of the arms thereof, the two condensers being connected together for simultaneous adjustment only, and a capacity in another arm of said Wheatstone bridge arrangeinent, said condensers being relatively formed to co-operate with said capacity to progressively unbalance the bridge by the simultaneous adjustment of said condensers in one direction, and to progressively restore the bridge to a more balanced condition by adjustment in the opposite direction.

7 A structure as specified in clai m 6, in combination with other elements forming with said WVheatstone bridge arrangement a radio circuit which can be tuned for different wave lengths by the said simultaneous adjustment of said condensers, whereby there will be a greater unbalance of the bridge for some wave lengths thanrfor others.

8. A structure as specified in claim 6, in

combination with elements forming with said Wheatstone bridge arrangementa radio receiving apparatus which can be tuned for different wave lengths by the said simultaneous adjustment of said condensers, and

said capacity being an adjustable condenser which can be set at a desired fixed adjustment for all adjustments of said two condensers.

9. A structure as specified in claim 6, said capacity being an adjustable condenser which can be set at a desired fixed adjustment for all adjustments of said two condensers. I

Specification signed this 10th day of April, 1925.

BYRON B. MINNIUM. 

